Over the past 25 years, the aviation industry has been the beneficiary of improved storm mapping systems. See U.S. Pat. Nos. 4,023,408, 4,395,906 and 6,347,549. Those storm mapping systems took advantage of the correlation between thunderstorms and lightning discharges. The violent air currents that are hazardous to aircraft flight produce the lightning discharge. The lightning discharge also generates electromagnetic waves. Directional receiving apparatus located on board an aircraft, can determine the direction of the lightning discharge. Some information is available about the distance or range of the discharge as well. By receiving and storing this direction and distance information, a map is formed from the stored data, to give the pilot a plan view image of the storm activity relative to the aircraft.
Notwithstanding the wide utility of aircraft carried storm mapping systems there is room for significant improvement.
Because of the limited area of the display it is necessary to pick and chose just what information to display and how to display it so as to convey to the user the most important information within the limits of the display. A solution to this desire should not be too rigid but instead allow the user to configure the display parameters to meet the current needs of the user.
In addition there is a need to provide for improved signal processing in respect of at least two different problems.
While lightning is a robust radiator of electromagnetic radiation, the environment in which these instruments are used is subject to a wide variety of noise sources, including sources located on the very same vehicle as is the storm mapping system. Earlier devices have attempted to accept signals generated by lightning while excluding signals derived from noise sources. We believe that there is room for much improvement in this area.
Even if we succeed in excluding all unwanted signals, there is still the problem of extracting the information which will allow us to accurately locate the lightning. For example, ranging to close in lightning is a substantial problem if the instrument must also be able to work at reasonable ranges, say significantly greater than 100 nautical miles. We believe we have made significant improvements in this area as well.
As we describe below we believe that we can filter noise based on the waveshape of the received signals. In order to be effective this requires that our data collection be capable of preserving information descriptive of the waveshape. To this end, the data the apparatus collects is capable of describing peaks in the waveforms and relating peaks in the three different channels to each other. This allows the system to obtain a measure of correlation between the loops signals and the sense signals. FIGS. 12 and 13 illustrate the difference between an instance where the signals are correlated (FIG. 12) and uncorrelated (FIG. 13). As is described our system requires the waveforms to be correlated within specific limits before the signals will be accepted as originating with lightning.
Further we recognize there are lightning originated signals which are not desirable. In particular most systems will have a range limit; a distance beyond which signals are of no interest. It is well known that the range of radio signals is quite variable. We have determined that the mechanism by which a radio signal has its range extended mangles the waveshape. FIG. 14 is an example of what we refer to as a “channeled” lightning signal. Comparing this figure to other figures of model lightning signals shows the waveform shown in FIG. 14 is more “wiggly” than the model lightning signals. The waveshape parameters collected by embodiments of the system allows the system to differentiate a model lightning waveform from the “channeled” waveforms such as illustrated in FIG. 14.